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Loss Of Power

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#1 squambug


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Posted 06 July 2018 - 03:14 PM

Hey y'all.  I am having a little trouble diagnosing some problems with my mini.



1975 Leyland 1000


Twin HS2

Maniflow LCB


I was having trouble with it running good and went over everything I can think of.  I checked compression, timing, dizzy points, valve gaps, replaced the fuel filter, and tweaked the carbs a ton.  I ended up buying a rebuild kit and rebuilt the carbs.


Main Problem:

Since then, I am only able to drive the mini about 5-10 minutes before it dies.  It starts by a small blip of power loss.  Not a slow decrease of loss, but a 1/2 second complete loss of power (torque).  The blips increase in frequency until it completely looses power and I am stranded.  Give it 10 minutes to 'rest' and I can limp back home.  I thought there might be an intake leak that when the car warms up gets worse.  I replaced the manifold gasket and ensured that it was good and tight, so I don't think it is there.  


I assume that something is off with the carb build, but am unsure.  I assume this is not a new experience and need some guidance on what to look at.


Some other things I have noticed, but don't think they contribute to the present problem:

  1. I have a wideband and see that I run really rich during idle, which I intentionally set to keep from going too lean during load conditions. I am running GY needles.  Don't know if this is a common for others.
  2. When letting off the gas after accelerating, the wideband runs really lean.  The dashpots are full.  I think I have heard about dashpot springs affecting this, but don't remember where I was reading it.
  3. I have noticed that the dashpots need oil very regularly.  Don't know if it is common to fill them once a week?

Sorry if some of these issues are basic, but as you probably can tell, I am from the other side of the pond and don't have the extensive background as y'all might have.


Let me know if there are any additional details that you want to know in order to help diagnose.


#2 sledgehammer


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Posted 06 July 2018 - 04:59 PM

first thing I would do is take fuel filler cap off - this will test if vent is working ok


next check fuel condition could be water / carp in it


is the carb /'s getting hot esp the float chamber area , as boiling fuel is a possibility - esp in hot weather


Edit ... also does your fuel have a lot of ethanol in it ?


ethanol tends to damage some metals / rubber , I had a new fuel pump & the new valves were shot , I think due to ethanol

another thing to look at is leads / coil / coil nose when they warm up they can start to fail

Edited by sledgehammer, 06 July 2018 - 06:50 PM.

#3 carbon


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Posted 06 July 2018 - 05:42 PM

+1 for Sledgehammers suggestions.

Sudden loss of power could be ignition. Are you running electronic or points?

PS. Set the idle to correct mixture, as this makes very little difference to mixture under load, if you're running lean under load then it is usually the needles which need changed.

Edited by carbon, 06 July 2018 - 05:46 PM.

#4 mini13


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Posted 06 July 2018 - 05:47 PM

Does sound like an ignition problem, I'd get it to fail and check for a spark.

This sound like an iffy condenser, or ifits electronic, the module.

#5 squambug


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Posted 06 July 2018 - 07:35 PM

@sledgehammer - I have opened the fuel cap while the car was running and have not noticed a difference. I would think there would be a change if that was the problem.  I would assume fuel is good as I have ran multiple tanks through while trying to diagnose.  We do have up to 10% ethanol in our fuel.  Nice picture.  My fuel pump is mechanical. I can't tell if yours is mechanical or not, but would there be a difference in ethanol messing with a mechanical/electrical pump?


I live in the south, which is really hot. However, I don't think I have ever had problems with fuel boiling.  Someone else suggested that, but am having a hard time thinking it is now just happening (after owning it for 3 years).  But I don't have a heat shield for my carbs.


I have wondered about the coil, but am ignorant of the details.


@carbon - I have points.  A very basic concept, but I have just ran with the idea of keeping the engine happy during load.  I have some M needles, which I would assume would be a step in the right direction if I have it running leaner during load compared to idle.


@mini13 - I would like to get it to fail when in the drive, but only happens when I am driving it.  I could drive it till it fails and then check for spark, but don't want to get too stranded right now ;)

#6 spin


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Posted 06 July 2018 - 08:45 PM

Attached is an old SpeedSport SU tuning book


This may help with some of you carb. questions

Attached Files

#7 Retroman


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Posted 06 July 2018 - 09:25 PM

Could be the coil and most condensers are not good these days and it may be that,


They only have about 1/2 the wire in them that they should, I will not supply them (only resin filled with 3m wire)


I would also question plug leads, plugs and plug gaps


NGK BP5ES plugs gapped to 0.025" points set at 0.015"


You should be OK with GY needles, they are a tadge weaker mid and top than M


The dashpots should not be using anywhere near as much oil, it should last a lot longer.  When you fill them you should only put oil in the centre tube where the damper goes, and then only 1/2 fill that. Use engine oil or Genuine Su damper oil. I would suggest 2 new dampers.

#8 squambug


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Posted 10 July 2018 - 04:19 PM

@spin - thanks for the resource.  Always good to have those extra guides.


@Retroman - I just ordered some new parts, including a coil and condenser.  So we'll see if it is one of those.  I have BP6ES plugs in right now (sounds like the 5 is a little hotter than the 6).  I included the BP5ES in the order.  I have used a 3 in 1 oil previously, but have used the SU specific oil recently. It does seem like it leaks too much.  I have read about filling not to the very top.  -New dampers are also in order :)


I'll play around with decreasing the richness to about 12.5 during idle and see how that looks like during full throttle.  I do have a set of M needles, and will see if need those or not depending on the test.


Just waiting now on the Minispares order.

#9 spin


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Posted 10 July 2018 - 09:37 PM

Like Retroman said you should be fine with GY/M needles.


In the SpeedSport bk Appendix 1 page 31 under  998 Austin Mini  64

you'll see those needles listed.

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